(S)-pyroglutamic acid, (S)-malic acid, and (S)-serine as useful starting materials in the synthesis of enantiopure hydroxyamidines

The synthesis of four enantiopure hydroxyamidines is described. One amidine was obtained from (S)-pyroglutamic acid. Its key step involved the additio n of phenylmagnesium bromide to the corresponding ester, affording the tert iary alcohol without detectable racemization. The second eventually transfo rmed into the corresponding amidines. amidine was obtained by coupling of a n (S)-malic acid derived N-acyliminium ion with beta-naphthol. The other am idines were obtained from an (S)-serine-derived imide which was reduced to two diastereomeric lactams that were eventually transformed into the corres ponding amidines.